Star Wars Galaxies started out with a 20 person group as the default. Early on, this could mean a group of 20 people running around on a planet ganking alien beasts that would take several minutes to solo. Sometimes, this meant gathering outside a place with tough-mobs like Fort-Tusken and killing everything that came out of there. There were even multiple 20-person groups there sometimes. This made you feel like a small part of an army. But you know what? You felt powerful because the group is powerful. You were a very small part of a very powerful force.
Five years later, Jedi’s had a boss unique to them and them alone. In order to obtain the best cloak in the game, each Jedi was forced to face two bosses solo. Anyone could stand and watch the Jedi fight these bosses, but no one could help. Unless a player read strategies ahead of time, they would fail both fights. Even when someone knew of strategies that worked for fighting these bosses, it was still a difficult set of fights. Complaints from players on the forums about the absurd difficulty of the fights only served to make the eventual victory more sweet. You felt powerful because you knew you had become skilled as a player.
Feeling skilled and feeling powerful. Can these two feelings exist in the same combat scenario? To me it seems they are at odds. The larger the group becomes, the greater the diffusion of responsibility a player feels. Too big a group, with a role shared by too many others in the group (like DPS in a raid) and I feel as though I don’t matter at all.